This invention relates generally to medical imaging systems and more particularly to a method and system for compensating for misalignment of image data sets caused by patient stretcher deflection.
Medical imaging requires accurate and repeatable positioning of the patient for a scan and a table that facilitates minimizing attenuation of the gamma radiation. However, in medical imaging systems using, for example, a large field-of-view (FOV) gamma camera, the patient stretcher may experience sag when performing a whole-body Single Photon Emission Tomography (SPECT) scan. The sag condition may cause displacement of images acquired at different stretcher positions during the scanning procedure.
One known method of reducing patient stretcher sag is to provide a reinforced table such that the vertical alignment within the imaging system can be maintained. However, when a patient is imaged using a wide FOV imaging system the patient stretcher is extended to accommodate the axial length of imaging system. A reinforced table may still not be sufficient to eliminate patient stretcher sag when a larger patient is being imaged. While utilizing a reinforced table is an option, fabricating a table having the increased stiffness required to eliminate patient stretcher sag may be relatively expensive. Moreover, it is advantageous to make the patient stretcher as thin as possible so that the detectors may be as close to the patient when directly underneath the patient as the spatial resolution deteriorate with distance. Additionally, it is advantageous to make the patient stretcher as radiation transparent as possible so as to minimize its interference with the measurement. Commonly patient stretchers are made of thin structure of composite material.
Another known method for correcting table sag is utilized in a multi-modality imaging system. This method includes utilizing a plurality of sensors that are installed downstream from the first modality in the multi-modality imaging system. The plurality of sensors identify the stretcher sag that occurs between each imaging system in the dual-modality imaging system and at a point furthest downstream from where the stretcher is inserted into the dual-modality imaging system. While this method is effective for identifying stretcher sag in a dual-modality imaging system, using multiple sensors in a single modality imaging system may increase the cost of the overall single-modality imaging system without necessarily increasing the accuracy of the stretcher sag measurement and therefore may not improve the ability of the single-modality imaging systems to compensate for misalignment of image data sets caused by the stretcher deflection.